This invention relates to a vehicle anti-theft system, and, more particularly, to an anti-theft system that is passive in the sense that it operates automatically when a user leaves the vehicle to protect the vehicle from unauthorized use.
Vehicle thefts, particularly thefts of passenger automobiles, represent a significant crime problem in this and other countries of the world. Many thefts are perpetrated by individuals who simply use the vehicle for a short period of time while others are perpetrated by individuals who take the vehicle for the purpose of realizing a profit from the eventual sale of the vehicle or its parts. In either case, the level of skill of the typical thief has risen to a point where present-day, factory installed vehicle anti-theft equipment is simply not sufficient to present any real obstacle to a taking. As a result, an increasingly large number of vehicle owners are relying upon specially installed anti-theft equipment to provide greater protection against the unauthorized use or loss of their vehicles.
The presently available vehicle anti-theft devices and systems vary widely in complexity, cost and in the amount of protection provided. One of the simplest of such devices is known as an "ignition kill" switch. This switch is typically hidden inside the vehicle and enables a user to disconnect the vehicle ignition system from its source of power, typically the vehicle battery, thereby to prevent the vehicle from being started. Other systems include an alarm or siren that can be set by the user so that an audible alarm will sound if a vehicle door or compartment is opened. Such alarm systems are typically set as the user leaves the vehicle and disabled as the user enters the vehicle using a key switch mounted outside the vehicle. Still other systems combine ignition kill devices with alarms or sirens to discourage both intrusions into and uses of the vehicle.
Although many of these prior systems tend to discourage the unskilled thief, they provide only a minimum amount of resistance to the skilled thief. For example, with the ignition kill switch, a thief, upon realizing that the vehicle will not start, will often search for, find and activate the inside switch to enable the vehicle to be started. Also, those systems that are enabled and disabled by an outside key switch can typically be disabled in one way or another by tampering with the outside switch. This can be accomplished, for example, by cutting, crossing, grounding or applying battery voltage to one or both of the wires extending to the outside key switch. Clearly, if a system can be defeated in such a manner, its effectiveness is greatly diminished.
Additionally, most prior systems are somewhat inconvenient to use because they require some form of positive action by the user upon leaving the vehicle, most typically the activation of the outside key switch, in order to set the system in condition to protect the vehicle. If the user is hurried, or if the vehicle is being left in a location that the user feels is relatively safe, the user will often not take the time or forget to set the system thereby leaving the vehicle unprotected.
Because of the latter problem, some anti-theft systems have been proposed that utilize timers that are activated in response to a typical exiting condition, such as turning the ignition key switch off. After a predetermined period of time has expired, the timer automatically sets the system in condition to protect the vehicle. Timers of this sort not only add to the cost of the systems, but also are inconvenient in that they require that the user fully exit the vehicle in the predetermined period of time. If the user requires more than the predetermined period of time to exit the vehicle because, for example, several passengers are exiting or packages are to be loaded or unloaded, the system must be disabled in order to prevent the sounding of an alarm.